In this paper we present surface dilatational properties of soy globulins (P-conglycinin, glycinin, and reduced glycinin with 10 mM of dithiothreitol (DTT)) adsorbed on the air-water interface, as a function of adsorption time. The surface rheological parameters (surface dilatational modulus, E, its elastic and viscous components, and phase angle) were measured as a function of protein concentration (ranging from 1 to 1 x 10(-3)%, wt/wt) at pH 2.0 and 5.0. We found that the surface dilatational modulus, E, increases with time, theta. This phenomenon has been related to protein adsorption, unfolding, and/or protein-protein interactions (at long-term adsorption). The dilatational properties of the adsorbed films depend on the molecular structure of the protein, the pH, and on the protein concentration in the aqueous phase. Soy globulins are adsorbed at the air-water interface with different degrees of association at different concentrations in the bulk phase and at different aqueous phase pH. (c) 2004 Elsevier Ltd. All rights reserved.